Large aperture photographic lens system

ABSTRACT

A large aperture photographic lens system comprising six components of seven lenses wherein flare due to coma at intermediate field angles has been eliminated by so adapting as to satisfy the following conditions: 
     
         (1)    0.9 &lt; r.sub.11 /r.sub.9 &lt; 1.05 ,                                   
 
    
                                  r 9    &gt; 0.55f                            
(2)    0.95 &lt; d 8  /d 10  &lt; 1.25                                    
(3)    1 &lt; r 5  /r 4  &lt; 1.3                                         
(4)    0.03f &lt; d 4  &lt; 0.05f                                            
(5)    n 1 , n 2 , n 5 , n 6 , n 7  &gt; 1.75

BACKGROUND OF THE INVENTION

a. Field of the Invention

The present invention relates to a variant type of Gauss photographic lens with an aperture ratio of 1.2 and a field angle of about 43° which is intended for use with 35 mm single-lens reflex photographic cameras.

B. Description of the Prior Art

Conventional Gauss type lenses had a great defect that flare was produced due to coma at intermediate field angles.

SUMMARY OF THE INVENTION

A general object of the present invention is to provide a compact photographic lens system of the above-mentioned Gauss type wherein said flare due to coma is favourably corrected at intermediate field angles.

The photographic lens system according to the present invention comprises six components of seven lenses wherein the first component is a positive meniscus lens, the second component is a positive meniscus lens, the third component is a negative meniscus lens, the fourth component is a cemented doublet lens composed of a negative lens and a positive lens, the fifth component is a positive meniscus lens, a sixth component is a positive lens. The lens system according to the present invention satisfies the following conditions(1) 0.9 < r₁₁ /r₉ < 1.05 , 9 > 0.55f(2) 0.95 < d₈ /d₁₀ < 1.25(3) 1 < r₅ /r₄ < 1.3(4) 0.03f < d₄ < 0.05f(5) n₁, n₂, n₅, n₆, n₇ > 1.75

Wherein the reference symbols denote as defined below:

f: focal length of the entire lens system

r₄, r₅, r₉ and r₁₁ : radii of curvature of the image side surface of the second lens, the object side surface of the third lens, the image side surface of the fourth lens component and the image side surface of the fifth lens respectively.

d₄ : air space between the second lens and the third lens

d₈ and d₁₀ : thicknesses of the image side lens of the fourth component and the fifth lens respectively

n₁, n₂, n₅, n₆ and n₇ : refractive indices of the first lens, the second lens, the image side lens of the fourth component, the fifth lens and the sixth lens respectively.

Now, the significance of the above-mentioned conditions will be described below:

When a large radius of curvature |r₉ | is selected for the image side surface of the fourth lens as defined in condition 1 on the assumption that the refractive power of the fourth component is kept at a constant value, it is possible to select a large value of r₇ as the radius of curvature for the object side surface of the fourth component. For reducing flare, it is effective to select such a large value of |r₇ |. Further, the flare can be corrected more favourably by selecting small value of |r₁₁ | within the range specified by condition 1. If the value of r₁₁ /r₉ is selected below the lower limit of condition 1, spherical aberration can hardly be corrected. When, on the other hand, the value of r₁₁ /r₉ exceeds the upper limit of condition 1, it is impossible to obtain sufficient effect for correcting flare.

According to condition 2, a small value of d₈ is selected as the thickness of the image side lens of the fourth component, while a large value of d₁₀ is adopted as the thickness of the fifth lens. This measure serves for further enhancing the above-described effect of condition 1. If the value of d₈ /d₁₀ is below the lower limit of condition 2, spherical aberration will be aggravated. When, on the other hand, the value of d₈ /d₁₀ exceeds the upper limit of condition 2, it will be impossible to correct flare to a sufficient degree.

Condition 3, which can exhibit sufficient effect in combination with condition 4, is required for favourably correcting coma and astigmatism. If the value of r₅ /r₄ is selected below the lower limit of condition 3, spherical aberration can not be corrected to a sufficient degree. When, on the other hand, the value of r₅ /r₄ exceeds the upper limit of condition 3, coma will be aggravated and curvature of field can not be corrected sufficiently.

Condition 4 which has been adopted in combination with condition 3 as is already described above is required for selecting relatively large value of d₄ as the air space between the second lens and the third lens for the purpose of enhancing the correcting effect obtained by condition 3. Hence, it will be impossible to obtain sufficient correcting effect for coma and astigmatism if the value of d₄ is selected below the lower limit of this condition. When, in contrast; the value of d₄ exceeds the upper limit of condition 4, lateral chromatic aberration will be aggravated to an undesirable degree.

Finally, condition 5 is necessary both for favourably correcting spherical aberration and for minimizing Petzval's sum. In contrast to the fact that the above-mentioned conditions 1 through 4 are required with a view to correcting aberrations for offaxial rays, condition 5 is necessary for favourably correcting aberrations for paraxial rays and minimizing Petzval's sum. Therefore, these effects will not be obtained if the refractive indices of respective lenses are selected outside the range defined by condition 5. When glass with high refractive index is used as material of the first and second lenses in order to satisfy condition 1, it is impossible to design these lenses so as to have large Abbe's numbers. In order to favourably correct lateral chromatic aberration under such a restriction, it is required to design the image side lens of the fourth component, fifth lens and sixth lens in such a manner that they have Abbe's numbers ν₅, ν₆ and ν₇ which are close to Abbe's numbers ν₁ and ν₂ of the first and second lenses. In view of this requirement, it is preferable to select these Abbe's numbers within the range of ν₁, ν₂, ν₅, ν₆ and ν₇ < 50.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view illustrating the composition of a large aperture lens system according to the present invention;

FIG. 2A through FIG. 2C illustrate curves showing the aberration characteristic of the embodiment 1;

FIG. 3A through FIG. 3C show graphs illustrating the aberration characteristic of the embodiment 2; and

FIG. 4A through FIG. 4C show graphs illustrating the aberration characteristic of the embodiment 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, some numerical data of the lens system according to the present invention will be exemplified below:Embodiment 1__________________________________________________________________________ f = 1.0 , f_(B) = 0.7066 , F/1.2r₁ = 0.8731 d₁ = 1.034 n₁ = 1.8061 ν₁ = 40.9r₂ = 3.5977 d₂ = 0.0023r₃ = 0.4580 d₃ = 0.0982 n₂ = 1.8061 ν₂ = 40.9r₄ = 0.7210 d₄ = 0.0454r₅ = 0.8444 d₅ = 0.0268 n₃ = 1.7847 ν₃ = 26.2r₆ = 0.3054 d₆ = 0.3200r₇ = -0.3510 d₇ = 0.0268 n₄ = 1.78472 ν₄ = 25.7r₈ = 3.2095 d₈ = 0.1327 n₅ = 1.79952 ν₅ = 42.2r₉ = -0.6036 d₉ = 0.0018r₁₀ = -2.3687 d₁₀ = 0.1107 n₆ = 1.79952 ν₆ = 42.2r₁₁ = -0.6074 d₁₁ = 0.0023r₁₂ = 1.9981 d₁₂ = 0.0504 n₇ = 1.7859 ν₇ = 44.2r₁₃ = -5.2395__________________________________________________________________________Embodiment 2__________________________________________________________________________ f = 1 , f_(B) = 0.6910 , F/1.2r₁ = 0.8135 d₁ = 0.0887 n₁ = 1.8061 ν₁ = 40.9r₂ = 2.8782 d₂ = 0.0023r₃ = 0.4419 d₃ = 0.1071 n₂ = 1.8061 ν₂ = 40.9r₄ = 0.6246 d₄ = 0.0339r₅ = 0.6965 d₅ = 0.0268 n₃ = 1.78472 ν₃ = 25.7r₆ = 0.2948 d₆ = 0.3262r₇ = -0.3460 d₇ = 0.0268 n₄ = 1.78472 ν₄ = 25.7r₈ = 2.6761 d₈ = 0.1178 n₅ = 1.8061 ν₅ = 40.9r₉ = -0.6001 d₉ = 0.0018r₁₀ = -1.6420 d₁₀ = 0.1184 n₆ = 1.7859 ν₆ = 44.2r₁₁ = -0.5630 d₁₁ = 0.0023r₁₂ = 1.7856 d₁₂ = 0.0513 n₇ = 1.79952 ν₇ = 42.2r₁₃ = -5.3612__________________________________________________________________________Embodiment 3__________________________________________________________________________ f = 1 , f_(B) = 0.6912 , F/1.2r₁ = 0.8267 d₁ = 0.0888 n₁ = 1.8061 ν₁ = 40.9r₂ = 3.4012 d₂ = 0.0023r₃ = 0.4529 d₃ = 0.1072 n₂ = 1.8061 ν₂ = 40.9r₄ = 0.7059 d₄ = 0.0341r₅ = 0.8472 d₅ = 0.0268 n₃ = 1.78472 ν₃ = 25.7r₆ = 0.3014 d₆ = 0.3211r₇ = -0.3541 d₇ = 0.0268 n₄ = 1.78472 ν₄ = 25.7r₈ = 6.4741 d₈ = 0.1179 n₅ = 1.8061 ν₅ = 40.9r₉ = -0.6131 d₉ = 0.0019r₁₀ = -1.7444 d₁₀ = 0.1184 n₆ = 1.7859 ν₆ = 44.2r₁₁ = -0.5707 d₁₁ = 0.0023r₁₂ = 1.8066 d₁₂ = 0.0513 n₇ = 1.79952 ν₇ = 42.2r₁₃ = -5.3646__________________________________________________________________________

wherein reference symbols r₁ through r₁₃ represent radii of curvature of respective lens surfaces, d₁ through d₁₂ denote thicknesses of respective lenses and distances between respective lenses, n₁ through n₇ indicate refractive indices of the lenses and ν₁ through ν₇ designate Abbe's number. Seidel's coefficients of the above-mentioned embodiments will be listed below:

    Embodiment 1                                                                   B         F        C         P       E                                         ______________________________________                                         1    0.3713   0.0924   0.0230  0.5112  0.1329                                  2    0.0813   -0.2375  0.6939  -0.1241 -1.6650                                 3    0.0296   0.0065   0.0014  0.9745  0.2148                                  4    0.0654   -0.2745  1.1533  -0.6190 -2.2444                                 5    -0.1940  0.5314   -1.4553 0.5207  2.5594                                  6    -1.0751  -0.3186  -0.0944 -1.4397 -0.4547                                 7    -1.7189  -0.7705  -0.3454 -1.2527 0.7163                                  8    0.0081   0.0120   0.0179  0.0014  0.0288                                  9    0.1664   -0.1318  0.1043  0.7361  -0.6655                                 10   0.0002   -0.0013  0.0094  -0.1876 1.2830                                  11   1.7270   -0.1622  0.0152  0.7315  -0.0701                                 12   -0.0138  0.0692   -0.3479 0.2202  0.6417                                  13   0.6545   -0.3469  0.1839  0.0840  -0.1420                                 Ε                                                                           0.1018   0.0091   -0.0406 0.1566  0.3353                                  ______________________________________                                         Embodiment 2                                                                        B        F        C       P       E                                       ______________________________________                                         1    0.4590   0.0928   0.0188  0.5486  0.1147                                  2    0.0621   -0.2005  0.6472  -0.1551 -1.5886                                 3    0.0553   0.0101   0.0018  1.0100  0.1842                                  4    0.0093   -0.0924  0.9149  -0.7146 -1.9835                                 5    -0.0595  0.2611   -1.1450 0.6313  2.2526                                  6    -1.0937  -0.2974  -0.0809 -1.4829 -0.4252                                 7    -1.8167  0.7881   -0.3419 -1.2708 0.6996                                  8    0.0113   0.0172   0.0262  0.0025  0.0439                                  9    0.1706   -0.1427  0.1194  0.7437  -0.7219                                 10   -0.0034  0.0130   -0.0499 -0.2680 1.2212                                  11   1.7282   -0.1288  0.0096  0.7816  -0.0590                                 12   -0.0073  0.0508   -0.3538 0.2488  0.7317                                  13   0.6841   -0.3440  0.1866  0.0829  -0.1462                                 Ε                                                                           0.1495   0.0272   -0.0469 0.1581  0.3234                                  ______________________________________                                         Embodiment 3                                                                        B        F        C       P       E                                       ______________________________________                                         1    0.4374   0.0966   0.0213  0.5399  0.1240                                  2    0.0946   -0.2639  0.7367  -0.1312 -1.6900                                 3    -0.0020  -0.0005  -0.0001 0.9855  0.2251                                  4    0.0899   -0.3364  1.2582  -0.6323 -2.3414                                 5    -0.2478  0.6243   -1.5725 0.5190  2.6536                                  6    - 1.0637 -0.3068  -0.0885 -1.4588 -0.4462                                 7    -1.7187  0.7783   -0.3525 -1.2417 0.7219                                  8    0.0070   0.0122   0.0212  0.0010  0.0386                                  9    0.1541   -0.1349  0.1182  0.7280  -0.7411                                 10   -0.0019  0.0081   -0.0351 -0.2523 1.2398                                  11   1.7167   -0.1525  0.0136  0.7711  -0.0697                                 12   -0.0073  0.0506   -0.3512 0.2459  0.7310                                  13   0.6365   -0.3507  0.1932  0.0828  -0.1521                                 Ε                                                                           0.0948   0.0245   -0.0375 0.1569  0.2935                                  ______________________________________                                                B:      spherical aberration                                                   F:      Coma                                                                   C:      astigmatism                                                            P:      Petzval's sum                                                          E:      distortion                                                      ______________________________________                                    

As is clearly understood from the foregoing descriptions, the present invention provides a compact lens system for photographic cameras which has high aperture ratio and which is capable of correcting aberrations very effectively. 

I claim:
 1. A large aperture photographic lens system comprising a first positive meniscus lens, a second positive meniscus lens, a third negative meniscus lens, a fourth cemented doublet lens component consisting of a negative lens and a positive lens, a fifth positive meniscus lens and sixth positive lens, and said large aperture photographic lens system satisfying the following conditions:

    (1)    0.9 < r.sub.11 /r.sub.9 < 1.05 ,                                                                    |r.sub. 9 | > 0.55f              (2)    0.95 < d.sub.8 /d.sub.10 < 1.25                                         (3)    1 < r.sub.5 /r.sub.4 < 1.3                                              (4)    0.03f < d.sub.4 < 0.05f                                                 (5)    n.sub.1, n.sub.2, n.sub.5, n.sub.6, n.sub.7 > 1.75                 

wherein reference symbol f represents the focal length of the entire lens system, reference symbols r₄, r₅, r₉ and r₁₁ represent respective radii of curvature of the image side surface of said second lens, the object side surface of said third lens, the image side surface of said fourth component and the image side surface of said fifth lens, reference symbol d₄ represents the air space between the second lens and the third lens, reference symbols d₈ and d₁₀ represent respective thicknesses of the image side lens of said fourth component and the fifth lens and reference symbols n₁, n₂, n₅, n₆ and n₇ represent respective refractive indices of said first lens, said second lens, the image side lens of said fourth component, said fifth lens and said sixth lens.
 2. A large aperture photographic lens system comprising a first positive meniscus lens, a second positive meniscus lens, a third negative meniscus lens, a fourth cemented doublet lens component consisting of a negative lens and a positive lens, a fifth positive meniscus lens and sixth positive lens, and said large aperture photographic lens system having the following numerical data:

         f = 1.0 ,   f.sub.B =                                                                             0.7066 ,  F/1.2                                        r.sub.1 =                                                                           0.8731                                                                         d.sub.1 = 1.034    n.sub.1 = 1.8061                                                                           ν.sub.1 = 40.9                          r.sub.2 =                                                                           3.5977                                                                         d.sub.2 = 0.0023                                                          r.sub.3 =                                                                           0.4580                                                                         d.sub.3 = 0.0982   n.sub.2 = 1.8061                                                                           ν.sub.2 = 40.9                          r.sub.4 =                                                                           0.7210                                                                         d.sub.4 = 0.0454                                                          r.sub.5 =                                                                           0.8444                                                                         d.sub.5 = 0.0268   n.sub.3 = 1.7847                                                                           ν.sub.3 = 26.2                          r.sub.6 =                                                                           0.3054                                                                         d.sub.6 = 0.3200                                                          r.sub.7 =                                                                           -0.3510                                                                        d.sub.7 = 0.0268   n.sub.4 = 1.78472                                                                          ν.sub.4 = 25.7                          r.sub.8 =                                                                           3.2095                                                                         d.sub.8 = 0.1327   n.sub.5 = 1.79952                                                                          ν.sub.5 = 42.2                          r.sub.9  =                                                                          -0.6036                                                                        d.sub.9 = 0.0018                                                          r.sub.10 =                                                                          -2.3687                                                                        d.sub.10 = 0.1107  n.sub.6 = 1.79952                                                                          ν.sub.6 = 42.2                          r.sub.11 =                                                                          -0.6074                                                                        d.sub.11 = 0.0023                                                         r.sub.12 =                                                                          1.9981                                                                         d.sub.12 = 0.0504  n.sub.7 = 1.7859                                                                           ν.sub.7 = 44.2                          r.sub.13 =                                                                          -5.2395                                                              

wherein reference symbols r₁ through r₁₃ represent radii of curvature of respective lens surfaces, d₁ through d₁₂ denote thicknesses of respective lenses and distances between respective lenses, n₁ through n₇ indicate refractive indices of the lenses and ν₁ through ν₇ designate Abbe's number.
 3. A large aperture photographic lens system comprising a first positive meniscus lens, a second positive meniscus lens, a third negative meniscus lens, a fourth cemented doublet lens component consisting of a negative lens and a positive lens, a fifth positive meniscus lens and sixth positive lens, and said large aperture photographic lens system having the following numerical data:

         f = 1 ,     f.sub.B =                                                                             0.6910 ,  F/1.2                                        r.sub.1 =                                                                           0.8135                                                                         d.sub.1 = 0.0887   n.sub.1 = 1.8061                                                                           ν.sub.1 = 40.9                          r.sub.2 =                                                                           2.8782                                                                         d.sub.2 = 0.0023                                                          r.sub.3 =                                                                           0.4419                                                                         d.sub.3 = 0.1071   n.sub.2 = 1.8061                                                                           ν.sub.2 = 40.9                          r.sub.4 =                                                                           0.6246                                                                         d.sub.4 = 0.0339                                                          r.sub.5 =                                                                           0.6965                                                                         d.sub.5 = 0.0268   n.sub.3 = 1.78472                                                                          ν.sub.3 = 25.7                          r.sub.6 =                                                                           0.2948                                                                         d.sub.6 = 0.3262                                                          r.sub.7 =                                                                           -0.3460                                                                        d.sub.7 = 0.0268   n.sub.4 = 1.78472                                                                          ν.sub.4 = 25.7                          r.sub.8 =                                                                           2.6761                                                                         d.sub.8 = 0.1178   n.sub.5 = 1.8061                                                                           ν.sub.5 = 40.9                          r.sub.9  =                                                                          -0.6001                                                                        d.sub.9 = 0.0018                                                          r.sub.10 =                                                                          -1.6420                                                                        d.sub.10 = 0.1184  n.sub.6 = 1.7859                                                                           ν.sub.6 = 44.2                          r.sub.11 =                                                                          -0.5630                                                                        d.sub.11 = 0.0023                                                         r.sub.12 =                                                                          1.7856                                                                         d.sub.12 = 0.0513  n.sub.7 = 1.79952                                                                          ν.sub.7 = 42.2                          r.sub.13 =                                                                          -5.3612                                                              

wherein reference symbols r₁ through r₁₃ represent radii of curvature of respective lens surfaces, d₁ through d₁₂ denote thicknesses of respective lenses and distances between respective lenses, n₁ through n₇ indicate refractive indices of the lenses and ν₁ through ν₇ designate Abbe's number.
 4. A large aperture photographic lens system comprising a first positive meniscus lens, a second positive meniscus lens, a third negative meniscus lens, a fourth cemented doublet lens component consisting of a negative lens and a positive lens, a fifth positive meniscus lens and sixth positive lens, and said large aperture photographic lens system having the following numerical data:

         f = 1 ,     f.sub.B =                                                                             0.6912 ,  F/1.2                                        r.sub.1 =                                                                           0.8267                                                                         d.sub.1 = 0.0888   n.sub.1 = 1.8061                                                                           ν.sub.1 = 40.9                          r.sub.2 =                                                                           3.4012                                                                         d.sub.2 = 0.0023                                                          r.sub.3 =                                                                           0.4529                                                                         d.sub.3 = 0.1072   n.sub.2 = 1.8061                                                                           ν.sub.2 = 40.9                          r.sub.4 =                                                                           0.7059                                                                         d.sub.4 = 0.0341                                                          r.sub.5 =                                                                           0.8472                                                                         d.sub.5 = 0.0268   n.sub.3 = 1.78472                                                                          ν.sub.3 = 25.7                          r.sub.6 =                                                                           0.3014                                                                         d.sub.6 = 0.3211                                                          r.sub.7 =                                                                           -0.3541                                                                        d.sub.7 = 0.0268   n.sub.4 = 1.78472                                                                          ν.sub.4 = 25.7                          r.sub.8 =                                                                           6.4741                                                                         d.sub.8 = 0.1179   n.sub.5 = 1.8061                                                                           ν.sub.5 = 40.9                          r.sub.9  =                                                                          -0.6131                                                                        d.sub.9 = 0.0019                                                          r.sub.10 =                                                                          -1.7444                                                                        d.sub.10 = 0.1184  n.sub.6 = 1.7859                                                                           ν.sub.6 = 44.2                          r.sub.11 =                                                                          -0.5707                                                                        d.sub.11 = 0.0023                                                         r.sub.12 =                                                                          1.8066                                                                         d.sub.12 = 0.0513  n.sub.7 = 1.79952                                                                          ν.sub.7 = 42.2                          r.sub.13 =                                                                          -5.3646                                                              

wherein reference symbols r₁ through r₁₃ represent radii of curvature of respective lens surfaces, d₁ through d₁₂ denote thicknesses of respective lenses and distances between respective lenses, n₁ through n₇ indicate refractive indices of the lenses and ν₁ through ν₇ designate Abbe's number. 